Planarization method and photocurable composition

ABSTRACT

A substrate surface planarization method includes an arranging step of arranging a liquid curable composition onto a substrate surface having unevenness, a waiting step of waiting until the surface of the layer of the liquid curable composition becomes smooth, and a light exposure step of applying light to cure the layer of the liquid curable composition in this order. The arranging step includes a first arranging step of arranging a layer made of a first liquid curable composition (A1) containing at least a polymerizable compound (a1), and a second arranging step of arranging droplets of a second liquid curable composition (A2) containing at least a polymerizable compound (a2) onto the layer made of the first liquid curable composition (A1) by dropping the droplets discretely.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/320,906, filed May 14, 2021, which claims thebenefit of U.S. Provisional Patent Application No. 63/041,191, filedJun. 19, 2020. Both prior applications are hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a planarization method and aphotocurable composition.

Description of the Related Art

In photolithography steps for fabricating semiconductor devices, it isnecessary to smooth the substrate. For example, in an extremeultraviolet exposure technique (EUV), which is a photolithographytechnique that has attracted attention in recent years, unevenness ofthe substrate surface to be coated with a photoresist needs to be keptat 4 nm or less, since miniaturization reduces the depth of focus atwhich a projected image is formed. Also, in a nanoimprinting lithography(NIL) technique as another photolithography technique too, a degree ofplanarization comparable to that of EUV is required to improvefillability and line width accuracy.

The most common planarization technique in the semiconductor industry ischemical-mechanical polishing (CMP). CMP, which has been developedmainly for hard materials such as metals and dielectrics, has severaldrawbacks. Applying CMP to soft materials such as organic materialsrequires strict process condition control. There is also a problem inthat for concavities wider than several μm, excessive polishinggenerates concavities, thus resulting in incomplete planarization.

Another planarization technique is a spin-on-carbon (SOC) techniquecommonly used for 45-nm-node and more recent semiconductor devices. Inthe SOC technique, a photolithography step is performed by spin-coatinga precursor solution of a carbon material dissolved in an organicsolvent onto a substrate, spin-coating a spin-on-glass (SOG) layer ontothe SOC, and coating a photoresist onto the SOG. When the liquid carbonmaterial precursor solution is spin-coated onto the substrate havingunevenness, the unevenness is reduced by the liquid's step coveringeffect. The SOC technique exhibits an excellent effect on concavitieswhose depth/width ratio (A.R.) is approximately 1 or more (e.g.,concavities with a depth of 100 nm and a width of 100 nm), but theeffect weakens as the A.R. of concavities decreases under 1 (e.g., whenthe depth is 100 nm and the width is 1000 nm). This is because a liquidfilm to be spin-coated has the property of attempting to form a liquidsurface parallel to the substrate surface.

In view of this, an object of the present invention is to provide aplanarization method and a photocurable composition also capable ofplanarizing an uneven substrate having concavities larger in width thanin depth.

SUMMARY OF THE INVENTION

According to the present invention, a planarization method is providedwhich includes an arranging step of arranging a liquid curablecomposition onto a substrate surface having unevenness, a waiting stepof waiting until a surface of a layer of the liquid curable compositionbecomes smooth, and a light exposure step of applying light to cure thelayer of the liquid curable composition in this order, and in which thearranging step includes a first arranging step of arranging a layer madeof a first liquid curable composition (A1) containing at least apolymerizable compound (a1), and a second arranging step of arrangingdroplets of a second liquid curable composition (A2) containing at leasta polymerizable compound (a2) onto the layer made of the first liquidcurable composition (A1) by dropping the droplets discretely.

Also, according to the present invention, a planarization method isprovided which includes an arranging step of arranging a liquid curablecomposition onto a substrate surface having unevenness, a molding stepof bringing a mold that is transparent to light applied thereto and hasa smooth surface into contact with the liquid curable composition on asurface of the substrate, a light exposure step of applying light fromthe mold side to cure the liquid curable composition, and a releasingstep of detaching the mold from the cured composition in this order, andin which the arranging step includes a first arranging step of arranginga layer made of a first liquid curable composition (A1) containing atleast a polymerizable compound (a1), and a second arranging step ofarranging droplets of a second liquid curable composition (A2)containing at least a polymerizable compound (a2) onto the layer made ofthe first liquid curable composition (A1) by dropping the dropletsdiscretely.

Further, according to the present invention, there are provided thefirst liquid curable composition (A1), the second liquid curablecomposition (A2) and a set comprising these compositions for use in theabove planarization methods.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E and 1F illustrate an embodiment of theplanarization method according to the present invention.

FIGS. 2E, 2F and 2G illustrate another embodiment of the planarizationmethod according to the present invention.

FIG. 3 illustrates a theoretical calculation model of Marangoni forceand Laplace pressure.

FIG. 4 illustrates an axisymmetric model representing a state where adroplet of a liquid curable composition (A2) is dropped onto a substrateon which a liquid film of a liquid curable composition (A1) is formed.

DESCRIPTION OF THE EMBODIMENTS

According to the present invention, it is possible to provide aplanarization method and a photocurable composition capable ofplanarizing an uneven substrate having concavities larger in width thanin depth.

Embodiments of the present invention will be described below in detailwith reference to the drawings as appropriate. It is to be noted thatthe present invention is not limited to the embodiments to be describedbelow. Moreover, the scope of the present invention also encompassesembodiments obtained by making changes, modifications, or the like tothe embodiments to be described below as appropriate based on ordinaryknowledge of those skilled in the art without departing from the gist ofthe present invention.

Curable Compositions

A liquid curable composition (A1) according to this embodiment is acompound having at least a component (a1) being a polymerizable compoundand a component (d1) being a solvent. The liquid curable composition(A1) according to this embodiment may further contain a component (b1)being a photopolymerization initiator and a non-polymerizable compound(c1).

A liquid curable composition (A2) according to this embodiment is acompound having at least a component (a2) being a polymerizablecompound. The liquid curable composition (A2) according to thisembodiment may further contain a component (b2) being aphotopolymerization initiator, a non-polymerizable compound (c2), and acomponent (d2) being a solvent.

Also, in this description, a cured film means a film obtained bypolymerizing and thus curing a liquid curable composition on asubstrate.

Each component will be described in detail below.

Component (a): Polymerizable Compound

The components (a1) and (a2) are polymerizable compounds. In thefollowing, the components (a1) and (a2) will be referred to collectivelyas a component (a). Here, in this description, a polymerizable compoundis a compound that reacts with a polymerization factor (such as radical)generated from the component (b1) or (b2), which is aphotopolymerization initiator, to form a film made of a polymericcompound as a result of a chain reaction (polymerization reaction).

Examples of such a polymerizable compound include radical polymerizablecompounds. The component (a), which is a polymerizable compound, may bemade solely of one kind of polymerizable compound or made of a pluralityof kinds of polymerizable compounds.

The radical polymerizable compounds are preferably compounds having oneor more acryloyl groups or methacryloyl groups, i.e., (meth)acryliccompounds. Thus, it is preferable that the curable compositionsaccording to this embodiment contain a (meth)acrylic compound as thecomponent (a). It is more preferable that the main component of thecomponent (a) be the (meth)acrylic compound. It is most preferable thatthe entire component (a) be the (meth)acrylic compound. Note that whenthe main component of the component (a) is a (meth)acrylic compound asmentioned here, it means that 90 wt % or more of the component (a) isthe (meth)acrylic compound.

When the radical polymerizable compound is made of a plurality of kindsof compounds having one or more acryloyl groups or methacryloyl groups,it is preferable that the radical polymerizable compound contain amonofunctional (meth)acrylic monomer and a multifunctional (meth)acrylicmonomer. This is because a cured film with high mechanical strength canbe obtained by combining a monofunctional (meth)acrylic monomer and amultifunctional (meth)acrylic monomer.

Examples of monofunctional (meth)acrylic compounds having one acryloylgroup or methacryloyl group include, but are not limited to,phenoxyethyl (meth)acrylate, phenoxy-2-methylethyl (meth)acrylate,phenoxyethoxyethyl (meth)acrylate, 3-phenoxy-2-hydroxypropyl(meth)acrylate, 2-phenylphenoxyethyl (meth)acrylate,4-phenylphenoxyethyl (meth)acrylate, 3-(2-phenylphenyl)-2-hydroxypropyl(meth)acrylate, EO-modified p-cumylphenol (meth)acrylate,2-bromophenoxyethyl (meth)acrylate, 2,4-dibromophenoxyethyl(meth)acrylate, 2,4,6-tribromophenoxyethyl (meth)acrylate, EO-modifiedphenoxy (meth)acrylate, PO-modified phenoxy (meth)acrylate,polyoxyethylene nonylphenyl ether (meth)acrylate, isobornyl(meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl(meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, bornyl(meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentanyl(meth)acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl(meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloylmorpholine,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl(meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl(meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl(meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,isostearyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropyleneglycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate,ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate,methoxypolypropylene glycol (meth)acrylate, diacetone (meth)acrylamide,isobutoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, t-octyl(meth)acrylamide, dimethylaminoethyl (meth)acrylate, diethylaminoethyl(meth)acrylate, 7-amino-3,7-dimethyloctyl (meth)acrylate, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, and thelike.

Commercially-available products of the above monofunctional(meth)acrylic compounds include, but are not limited to: Aronix(registered trademark) M101, M102, M110, M111, M113, M117, M5700,TO-1317, M120, M150, and M156 (which are manufactured by TOAGOSEI CO.,LTD.); MEDOL10, MIBDOL10, CHDOL10, MMDOL30, MEDOL30, MIBDOL30, CHDOL30,LA, IBXA, 2-MTA, HPA, and Viscoat #150, #155, #158, #190, #192, #193,#220, #2000, #2100, and #2150 (which are manufactured by OSAKA ORGANICCHEMICAL INDUSTRY LTD.); LIGHT ACRYLATE BO-A, EC-A, DMP-A, THF-A, HOP-A,HOA-MPE, HOA-MPL, PO-A, P-200A, NP-4EA, and NP-8EA and EPOXY ESTERM-600A (which are manufactured by Kyoeisha Chemical Co., Ltd.); KAYARAD(registered trademark) TC110S, R-564, and R-128H (which are manufacturedby Nippon Kayaku Co., Ltd.); NK ester AMP-10G and AMP-20G (which aremanufactured by Shin-Nakamura Chemical Co., Ltd.); FA-511A, 512A, and513A (which are manufactured by Hitachi Chemical Co., Ltd.); PHE, CEA,PHE-2, PHE-4, BR-31, BR-31M, and BR-32 (which are manufactured byDAI-ICHI KOGYO SEIYAKU CO., LTD.); VP (which is manufactured by BASF);ACMO, DMAA, and DMAPAA (which are manufactured by KOHJIN); and the like.

Examples of multifunctional (meth)acrylic compounds having two or moreacryloyl groups or methacryloyl groups include, but are not limited to,trimethylolpropane di(meth)acrylate, trimethylolpropanetri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate,PO-modified trimethylolpropane tri(meth)acrylate, EO,PO-modifiedtrimethylolpropane tri(meth)acrylate, dimethyloltricyclodecanedi(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate,1,3-adamantanedimethanol di(meth)acrylate,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(acryloyloxy)isocyanurate, bis(hydroxymethyl)tricyclodecanedi(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, EO-modified2,2-bis(4-((meth)acryloxy)phenyl)propane, PO-modified2,2-bis(4-((meth)acryloxy)phenyl)propane, EO,PO-modified2,2-bis(4-((meth)acryloxy)phenyl)propane, and the like.

Commercially-available products of the above multifunctional(meth)acrylic compounds include, but are not limited to: Yupimer(registered trademark) UV SA1002 and SA2007 (which are manufactured byMitsubishi Chemical Corporation); Viscoat #195, #230, #215, #260,#335HP, #295, #300, #360, #700, GPT, and 3PA (which are manufactured byOSAKA ORGANIC CHEMICAL INDUSTRY LTD.); LIGHT ACRYLATE 4EG-A, 9EG-A,NP-A, DCP-A, BP-4EA, BP-4PA, TMP-A, PE-3A, PE-4A, and DPE-6A (which aremanufactured by Kyoeisha Chemical Co., Ltd.); KAYARAD (registeredtrademark) PET-30, TMPTA, R-604, DPHA, DPCA-20, -30, -60, and -120,HX-620, D-310, and D-330 (which are manufactured by Nippon Kayaku Co.,Ltd.); Aronix (registered trademark) M208, M210, M215, M220, M240, M305,M309, M310, M315, M325, and M400 (which are manufactured by TOAGOSEICO., LTD.); Ripoxy (registered trademark) VR-77, VR-60, and VR-90 (whichare manufactured by Showa High Polymer Co., Ltd.); and the like.

Note that the (meth)acrylate in the above compounds means an acrylate ora methacrylate having an alcohol residue equivalent thereto. A(meth)acryloyl group means an acryloyl group or a methacryloyl grouphaving an alcohol residue equivalent thereto. EO denotes ethylene oxide,and an EO-modified compound A refers to a compound in which a(meth)acrylic acid residue and an alcohol residue of the compound A arebonded to each other through the block structure of an ethylene oxidegroup. Also, PO denotes propylene oxide, and a PO-modified compound Brefers to a compound in which a (meth)acrylic acid residue and analcohol residue of the compound B are bonded to each other through theblock structure of a propylene oxide group.

Component (b): Photopolymerization Initiator

The components (b1) and (b2) are photopolymerization initiators. In thefollowing, the components (b1) and (b2) will be referred to collectivelyas a component (b).

In this description, a photopolymerization initiator is a compound thatgenerates the above-mentioned polymerization factor (radical) by sensinglight of predetermined wavelengths. Specifically, a photopolymerizationinitiator is a polymerization initiator (radical generating agent) thatgenerates a radical by means of light (a radiation such as infraredrays, visible rays, ultraviolet rays, far-ultraviolet rays, X rays, orcharged-particle beams including electron rays).

The component (b) may be made of one kind of photopolymerizationinitiator or made of a plurality of kinds of photopolymerizationinitiators.

Examples of the radical generating agent include, but are not limitedto:2,4,5-triarylimidazole dimers that may have substituents such as2-(o-chlorophenyl)-4,5-diphenylimidazole dimer,2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer,2-(o-fluorophenyl)-4,5-diphenylimidazole dimer, and 2-(o- orp-methoxyphenyl)-4,5-diphenylimidazole dimer; benzophenone andbenzophenone derivatives such asN,N′-tetramethyl-4,4′-diaminobenzophenone (Michler's ketone),N,N′-tetraethyl-4,4′-diaminobenzophenone,4-methoxy-4′-dimethylaminobenzophenone, 4-chlorobenzophenone,4,4′-dimethoxybenzophenone, and 4,4′-diaminobenzophenone; α-aminoaromatic ketone derivatives such as2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 and2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one; quinonessuch as 2-ethylanthraquinone, phenanthrenequinone,2-t-butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone,2,3-benzanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone,1-chloroanthraquinone, 2-methylanthraquinone, 1,4-naphthoquinone,9,10-phenanthraquinone, 2-methyl-1,4-naphthoquinone, and2,3-dimethylanthraquinone; benzoin ether derivatives such as benzoinmethyl ether, benzoin ethyl ether, and benzoin phenyl ether; benzoin andbenzoin derivatives such as methylbenzoin, ethylbenzoin, andpropylbenzoin; benzyl derivatives such as benzyl dimethyl ketal;acridine derivatives such as 9-phenylacridine and1,7-bis(9,9′-acridinyl)heptane; N-phenylglycine derivatives such asN-phenylglycine; acetophenone and acetophenone derivatives such as3-methylacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexylphenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone; thioxanthone andthioxanthone derivatives such as diethylthioxanthone,2-isopropylthioxanthone, and 2-chlorothioxanthone; acylphosphine oxidederivatives such as 2,4,6-trimethylbenzoyl diphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; oximeester derivatives such as 1,2-octanedione, 1-[4-(phenylthio)phenyl]-,2-(O-benzoyloxime) (trade name: Irgacure OXE01), ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, and 1-(O-acetyloxime)(trade name: Irgacure OXE02); xanthone; fluorenone; benzaldehyde;fluorene; anthraquinone; triphenylamine; carbazol;1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one;2-hydroxy-2-methyl-1-phenylpropane-1-one; and the like.

Commercially-available products of the above radical generating agentsinclude, but are not limited to, Irgacure 184, 369, 651, 500, 819, 907,784, and 2959, CGI-1700, -1750, and -1850, and CG24-61, Darocur 1116 and1173, Lucirin (registered trademark) TPO, LR8893, and LR8970 (which aremanufactured by BASF), Ubecryl P36 (manufactured by UCB), and the like.

It is preferable that the component (b) be an acylphosphine oxide-basedpolymerization initiator among these. Note that among the aboveexamples, the acylphosphine oxide-based polymerization initiator is anacylphosphine oxide compound such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphineoxide.

Advantageously, the blending ratio of the component (b), which is aphotopolymerization initiator, in the liquid curable compositions (A1)and (A2) is 0.1 wt % or more and 50 wt % or less with respect to thetotal of the component (a), the component (b), and the later-describedcomponent (c), i.e., the total weight of all components excluding thesolvent component (d). Further, the blending ratio is preferably 0.1 wt% or more and 20 wt % or less, and more preferably more than 10 wt % and20 wt % or less.

By setting the blending ratio of the component (b) at 0.1 wt % or morewith respect to the total of the component (a), the component (b), andthe component (c), the rate of curing of the composition is high, whichenables a good reaction efficiency. Also, by setting the blending ratioof the component (b) at 50 wt % or less with respect to the total of thecomponent (a), the component (b), and the component (c), the obtainedcured film can be a cured film having a certain degree of mechanicalstrength.

Component (c): Non-Polymerizable Compound

The components (c1) and (c2) are non-polymerizable compounds. In thefollowing, the components (c1) and (c2) will be referred to collectivelyas a component (c).

In addition to the above-described component (a) and component (b), theliquid curable compositions (A1) and (A2) according to this embodimentcan further contain a non-polymerizable compound as the component (c)according to various purposes within such an extent range that theeffect of the present invention is not impaired. Such a component (c)includes compounds that have neither a polymerizable functional groupsuch as a (meth)acryloyl group nor an ability to generate theabove-mentioned polymerization factor (radical) by sensing light of thepredetermined wavelengths. Examples include a sensitizer, a hydrogendonor, an internal release agent, a surfactant, an antioxidant, apolymer component, other additives, and so on. The component (c) maycontain two or more of the above compounds.

The sensitizer is a compound to be added as appropriate for the purposeof promoting the polymerization reaction and improving thepolymerization conversion. Examples of the sensitizer include asensitizing dye and the like.

The sensitizing dye is a compound that becomes excited by absorbinglight of particular wavelengths and interacts with thephotopolymerization initiator being the component (b). Note that theinteraction mentioned here is energy transfer, electron transfer, or thelike from the sensitizing dye in the excited state to thephotopolymerization initiator being the component (b).

Specific examples of the sensitizing dye include, but are not limitedto, an anthracene derivative, an anthraquinone derivative, a pyrenederivative, a perylene derivative, a carbazol derivative, a benzophenonederivative, a thioxanthone derivative, a xanthone derivative, a coumarinderivative, a phenothiazine derivative, a camphorquinone derivative, anacridine-based dye, a thiopyrylium salt-based dye, a merocyanine-baseddye, a quinoline-based dye, a styrylquinoline-based dye, aketocoumarin-based dye, a thioxanthene-based dye, a xanthene-based dye,an oxonol-based dye, a cyanine-based dye, a rhodamine-based dye, apyrylium salt-based dye, and the like.

One kind of sensitizer may be used alone, or a mixture of two or morekinds of sensitizers may be used.

The hydrogen donor is a compound that reacts with an initiation radicalgenerated from the component (b) being the photopolymerization initiatoror with the radical of a polymerization growth terminal to generate amore reactive radical. The hydrogen donor is preferably added when thecomponent (b) being the photopolymerization initiator is a photoradicalgenerating agent.

Specific examples of such a hydrogen donor include, but are not limitedto: amine compounds such as n-butylamine, di-n-butylamine,tri-n-butylphosphine, allylthiourea,s-benzylisothiouronium-p-toluenesulfinate, triethylamine,diethylaminoethyl methacrylate, triethylenetetramine,4,4′-bis(dialkylamino)benzophenone, N,N-dimethylaminobenzoic acid ethylester, N,N-dimethylaminobenzoic acid isoamyl ester,pentyl-4-dimethylaminobenzoate, triethanolamine, and N-phenylglycine;mercapto compounds such as 2-mercapto-N-phenylbenzimidazole andmercaptopropionic acid ester; and the like.

One kind of the hydrogen donors may be used alone, or a mixture of twoor more kinds thereof may be used. Also, the hydrogen donor may have thefunction of a sensitizer.

In addition to the above components, an internal release agent may beadded to the liquid curable composition for the purpose of reducing thestrength of the interfacial bond between a mold and a resist, i.e.,reducing the releasing force in a later-described releasing step. Inthis description, the internal addition type means that the mold releaseagent is added to the liquid curable composition in advance before astep of arranging the liquid curable composition.

As the internal release agent, surfactants such as a silicone-basedsurfactant, a fluorine-based surfactant, and a hydrocarbon-basedsurfactant, and the like are usable. Note that in the present invention,the internal release agent is not polymerizable.

The fluorine-based surfactant includes: a polyalkylene oxide (such aspolyethylene oxide or polypropylene oxide) adduct of an alcohol having aperfluoroalkyl group, a polyalkylene oxide (such as polyethylene oxideor polypropylene oxide) adduct of perfluoropolyether, and the like. Notethat the fluorine-based surfactant may have a hydroxyl group, an alkoxygroup, an alkyl group, an amino group, a thiol group, or the like onpart (e.g., terminal group) of its molecular structure.

A commercially-available product may be used as the fluorine-basedsurfactant. Examples of the commercially-available product include:MEGAFACE (registered trademark) F-444, TF-2066, TF-2067, and TF-2068(which are manufactured by DIC Corporation); Fluorad FC-430 and FC-431(which are manufactured by Sumitomo 3M Limited); SURFLON (registeredtrademark) S-382 (manufactured by AGC); EFTOP EF-122A, 122B, and 122C,EF-121, EF-126, EF-127, and MF-100 (which are manufactured by TohkemProducts Corporation); PF-636, PF-6320, PF-656, and PF-6520 (which aremanufactured by OMNOVA Solutions Inc.); UNIDYNE (registered trademark)DS-401, DS-403, and DS-451 (which are manufactured by DAIKIN INDUSTRIES,LTD); FTERGENT (registered trademark) 250, 251, 222F, and 208G (whichare manufactured by NEOS COMPANY LIMITED); and the like.

Alternatively, the internal release agent may be a hydrocarbon-basedsurfactant.

The hydrocarbon-based surfactant includes an alkyl alcohol polyalkyleneoxide adduct obtained by adding an alkylene oxide having 2 to 4 carbonatoms to an alkyl alcohol having 1 to 50 carbon atoms, and the like.

The alkyl alcohol polyalkylene oxide adduct includes a methyl alcoholethylene oxide adduct, a decyl alcohol ethylene oxide adduct, a laurylalcohol ethylene oxide adduct, a cetyl alcohol ethylene oxide adduct, astearyl alcohol ethylene oxide adduct, a stearyl alcohol ethyleneoxide/propylene oxide adduct, and the like. Note that the terminal groupof the alkyl alcohol polyalkylene oxide adduct is not limited to ahydroxyl group, which can be produced by simply adding a polyalkyleneoxide to an alkyl alcohol. This hydroxyl group may be substituted withanother substituent, e.g., a polar functional group such as a carboxylgroup, an amino group, a pyridyl group, a thiol group, or a silanolgroup or with a hydrophobic functional group such as an alkyl group oran alkoxy group.

A commercially-available product may be used as the alkyl alcoholpolyalkylene oxide adduct. Examples of the commercially-availableproduct include: polyoxyethylene methyl ethers (methyl alcohol ethyleneoxide adducts) manufactured by AOKI OIL INDUSTRIAL Co., Ltd. (BLAUNONMP-400, MP-550, and MP-1000); polyoxyethylene decyl ethers (decylalcohol ethylene oxide adducts) manufactured by AOKI OIL INDUSTRIAL Co.,Ltd. (FINESURF D-1303, D-1305, D-1307, and D-1310); a polyoxyethylenelauryl ether (lauryl alcohol ethylene oxide adduct) manufactured by AOKIOIL INDUSTRIAL Co., Ltd. (BLAUNON EL-1505); polyoxyethylene cetyl ethers(cetyl alcohol ethylene oxide adducts) manufactured by AOKI OILINDUSTRIAL Co., Ltd. (BLAUNON CH-305 and CH-310); polyoxyethylenestearyl ethers (stearyl alcohol ethylene oxide adducts) manufactured byAOKI OIL INDUSTRIAL Co., Ltd. (BLAUNON SR-705, SR-707, SR-715, SR-720,SR-730, and SR-750); random polymerization-type polyoxyethylenepolyoxypropylene stearyl ethers manufactured by AOKI OIL INDUSTRIAL Co.,Ltd. (BLAUNON SA-50/50 1000R and SA-30/70 2000R); a polyoxyethylenemethyl ether manufactured by BASF (Pluriol (registered trademark)A760E); polyoxyethylene alkyl ethers manufactured by Kao Corporation(EMULGEN series); and the like.

Among these hydrocarbon-based surfactants, the internal release agent ispreferably an alkyl alcohol polyalkylene oxide adduct and morepreferably a long-chain alkyl alcohol polyalkylene oxide adduct.

One kind of the internal release agents may be used alone, or a mixtureof two or more kinds thereof may be used.

Advantageously, the blending ratio of the component (c), which is anon-polymerizable compound, in the liquid curable composition is 0 wt %or more and 50 wt % or less with respect to the total of the component(a), the component (b), and the later-described component (c), i.e., thetotal weight of all components excluding the solvent. Further, theblending ratio is preferably 0.1 wt % or more and 50 wt % or less, andmore preferably 0.1 wt % or more and 20 wt % or less.

By setting the blending ratio of the component (c) at 50 wt % or lesswith respect to the total of the component (a), the component (b), andthe component (c), the obtained cured film can be a cured film having acertain degree of mechanical strength.

Component (d): Solvent

The components (d1) and (d2) are solvents. In the following, thecomponents (d1) and (d2) will be referred to collectively as a component(d).

The liquid curable composition (A1) according to this embodimentcontains the solvent component (d1). This is because a spin coatingmethod is preferable as a method of coating the liquid curablecomposition (A1) onto a substrate, as will be described later. For thisreason, the content of the solvent component (dl) is preferably 90 wt %or more and 99.99 wt % or less, and particularly preferably 99 wt % ormore and 99.9 wt % or less. As the solvent component (d1) of the liquidcurable composition (A1), a solvent is used in which the component (a1),the component (b1), and the component (c1) dissolve and which has alower surface tension than that of the mixture of the component (a1),the component (b1), and the component (c1). The lower the surfacetension of the solvent component (d1) is, the more even a film obtainedby a spin coating method will be. A more preferable solvent is a solventwith a boiling point of 80° C. or higher and 200° C. or lower at normalpressure. More preferably, the solvent is a solvent having at least oneof an ester structure, a ketone structure, a hydroxyl group, and anether structure. Specifically, the solvent is a single solvent selectedfrom propylene glycol monomethyl ether acetate, propylene glycolmonomethyl ether, cyclohexanone, 2-heptanone, γ-butyrolactone, andlactate ethyl, or a mixed solvent thereof.

The liquid curable composition (A2) according to this embodiment maycontain a solvent as the component (d2). The component (d2) to be addedto the liquid curable composition (A2) is not particularly limited aslong as it is a solvent in which the component (a2), the component (b2),and the component (c2) dissolve. A preferable solvent is a solvent witha boiling point of 80° C. or higher and 200° C. or lower at normalpressure. More preferably, the solvent is a solvent having at least oneof an ester structure, a ketone structure, a hydroxyl group, and anether structure. Specifically, the solvent is a single solvent selectedfrom propylene glycol monomethyl ether acetate, propylene glycolmonomethyl ether, cyclohexanone, 2-heptanone, γ-butyrolactone, andlactate ethyl, or a mixed solvent thereof.

Temperature during Blending of Curable Compositions

When the liquid curable compositions (A1) and (A2) according to thisembodiment are prepared, at least the component (a) and the component(b) are mixed and dissolved under a predetermined temperature condition.Specifically, the preparation is performed in a range of from 0° C. orhigher to 100° C. or lower. This applies also to the case where thecomponent (c) and the component (d) are contained.

Viscosity of Curable Compositions

It is preferable that each of the liquid curable compositions (A1) and(A2) according to this embodiment be liquid in the state without thesolvent (component (d)). This is because the surface of a liquid film ofthe mixed liquid curable composition or the liquid curable composition(A2) will become smooth more quickly from after the arranging step to awaiting step or from after the arranging step to a molding step, whichwill be described later.

The viscosity of the mixture of the components of the liquid curablecomposition (A1) according to this embodiment excluding the solvent(component (d)) at 25° C. is preferably 1 mPa·s or higher and 1,000mPa·s or lower. Also, the viscosity is more preferably 1 mPa·s or higherand 500 mPa·s or lower, and further preferably 1 mPa·s or higher and 100mPa·s or lower.

The viscosity of the mixture of the components of the liquid curablecomposition (A2) according to this embodiment excluding the solvent (ifthe component (d2) is contained) at 25° C. is preferably 1 mPa·s orhigher and 100 mPa·s or lower. Also, the viscosity is more preferably 1mPa·s or higher and 50 mPa·s or lower, and further preferably 1 mPa·s orhigher and 30 mPa·s or lower. By setting the viscosity at 100 mPa·s orlower, a small droplet of, e.g., 1 picoliter (pLP), can be dropped ontoa substrate surface by a later-described inkjet method.

The lower the viscosity of the liquid curable compositions (A1) and (A2)is, the more quickly the surface of a liquid film of the mixed liquidcurable composition will become smooth.

Also, when the curable compositions (A1) and (A2) are coated onto asubstrate, uneven coating is unlikely to occur by setting the viscosityat 1 mPa·s or higher.

Surface Tension of Liquid Curable Compositions

The liquid curable compositions (A1) and (A2) according to thisembodiment are preferably such that the surface tension of thecompositions with the components excluding the solvent (component (d))at 23° C. is 5 mN/m or higher and 70 mN/m or lower. Also, the surfacetension is more preferably 20 mN/m or higher and 50 mN/m or lower, andfurther preferably 20 mN/m or higher and 40 mN/m or lower. Here, thehigher the surface tension is, the more quickly the surface of a liquidfilm will become smooth.

Also, by setting the surface tension at 70 mN/m or lower, the cured filmto be obtained by curing the liquid curable compositions will be a curedfilm having a smooth surface.

In this embodiment, it is preferable that the surface tension of theliquid curable composition (A1) without its solvent (component (d1)) behigher than the surface tension of the liquid curable composition (A2)without its solvent (component (d)) in the case where a molding step isto be performed for the purpose of accelerating the planarization. Thisis because, after the arranging step in which droplets of the liquidcurable composition (A2) are dropped onto the liquid curable composition(A1), the spread of the liquid curable composition (A2) gets accelerated(the droplets spread over a larger region) by the later-describedMarangoni effect, thereby shortening the time of the later-describedwaiting step. It is also because, in the case where a mold is pressed,the time of filling after the molding step is shortened.

The Marangoni effect refers to the phenomenon in which the free surfaceof a liquid is moved by a local difference in surface tension (N.IMAISHI/Int. J. Microgravity Sci. No.31 Supplement 2014 (S5-S12)). Aliquid with a lower surface tension spreads so as to cover a largersurface by means of a difference in surface tension, i.e., surfaceenergy, as driving force. That is, by coating the entire substratesurface with the liquid curable composition (A1) with a higher surfacetension and then dropping the liquid curable composition (A2) with alower surface tension, the spread of the liquid curable composition (A2)will be accelerated. A film of the liquid curable composition (A1) ispreferably higher than the liquid curable composition (A2) by 1 mN/m ormore.

Contact Angle of Liquid Curable Compositions

The contact angle of the liquid curable compositions (A1) and (A2)according to this embodiment to a substrate surface is preferably 0° ormore and 90° or less and particularly preferably 0° or more and 30° orless when they are the compositions with the components excluding thesolvent (component (d)). If the contact angle is more than 90°, thewettability with a substrate surface is so low that a smooth liquid filmsurface cannot be obtained.

Impurities Included in Liquid Curable Compositions

It is preferable that the liquid curable compositions (A1) and (A2)according to this embodiment contain as few impurities as possible. Theimpurities mentioned here mean substances other the above-describedcomponent (a), component (b), component (c), and component (d).

It is therefore preferable that the liquid curable compositionsaccording to this embodiment be obtained through a purification step.Such a purification step is preferably filtration using a filter or thelike.

Specifically, in the case of performing filtration using a filter, it ispreferable to mix the above-described component (a) and component (b)and an additive component(s) to be added as needed and then filter themixture through a filter having a pore diameter of, for example, 0.001μm or larger and 5.0 μm or smaller. In the case of performing filtrationusing a filter, it is more preferable to perform the filtration in manystages or repeat the filtration many times. Also, the filtered liquidmay be filtered again. Filtration using a plurality of filters withdifferent pore diameters may be performed. As the filter to be used inthe filtration, a filter made of a polyethylene resin, a polypropyleneresin, a fluororesin, a nylon resin, or the like can be used, but thefilter is not particularly limited.

Through such a purification step, it is possible to remove impuritiessuch as particles included in the liquid curable compositions. Thus, itis possible to prevent generation of pattern defects due to impuritiessuch as particles unintendedly forming unevenness on the cured filmobtained after curing the liquid curable compositions.

Note that in the case of using the liquid curable compositions accordingto this embodiment to fabricate a semiconductor integrated circuit, itis preferable to avoid inclusion of impurities containing metallic atoms(metallic impurities) into the liquid curable compositions as much aspossible, in order not to impair the operation of the product. In such acase, the concentration of the metallic impurities contained in theliquid curable compositions is preferably 10 ppm or lower and morepreferably 100 ppb or lower.

Planarization Method

Next, a planarization method according to this embodiment will bedescribed using schematic cross-sectional views of FIGS. 1A to 1F (andFIGS. 2E to 2G). In these views, a substrate is depicted to have asmooth surface for the sake of simplicity.

The planarization method according to this embodiment includes:

-   -   an arranging step of arranging a liquid curable composition onto        a substrate surface having unevenness;    -   a waiting step of waiting until the surface of the layer of the        liquid curable composition becomes smooth; and    -   a light exposure step of applying light to cure the layer of the        liquid curable composition.

The thickness of a smooth film formed by the planarization methodaccording to this embodiment, i.e., a cured film obtained by curing theliquid curable composition, is preferably 1 to 10,000 nm at theconcavities on the substrate. As a result of the planarization, thethickness of the cured film at the convexities on the substrate issmaller than the thickness of the cured film at the concavities on thesubstrate, and the thickness difference is equivalent to the largestheight difference between the concavities and the convexities on thesubstrate.

First Arranging Step [1]

In this step (first arranging step [1]), as illustrated in FIGS. 1A and1B, a liquid curable composition (A1) 102 according to this embodimentdescribed above is arranged (coated) onto a substrate 101 to form acoated film. Note that this step (first arranging step [1]) can beomitted if the liquid curable composition (A2) can spread sufficientlyin a later-described second arranging step [2] and waiting step [3] andthus a smooth liquid film surface can be obtained.

The substrate 101 as the target on which to arrange the liquid curablecomposition (A1) 102 is a substrate to be processed, and a silicon waferis usually used. A layer to be processed may be formed on the substrate101. Another layer may further be formed between the substrate 101 andthe layer to be processed.

Note that in the present invention, the substrate 101 is not limited toa silicon wafer or a quartz substrate. The substrate 101 can also beselected from among those known as semiconductor device substrates madeof aluminum, a titanium-tungsten alloy, an aluminum-silicon alloy, analuminum-copper-silicon alloy, a silicon oxide, a silicon nitride, orthe like as desired.

On the substrate to be processed, there is unevenness originating fromsubstrate processing steps before the steps used in the presentinvention. The height difference between the concavities and theconvexities is about 1 to 1,000 nm, for example.

Note that the adhesiveness of the surface of the substrate 101 to beused (substrate to be processed) or of the layer to be processed withthe liquid curable compositions (A1) and (A2) may be improved beforehandby a surface treatment such as a silane coupling treatment, a silazanetreatment, or formation of an organic thin film. The surface of thesubstrate is a solid surface that does not get mixed with the liquidcurable composition (A1) or the liquid photocurable composition (A2).

In this embodiment, an inkjet method, a dip coating method, an air knifecoating method, a curtain coating method, a wire-bar coating method, agravure coating method, an extrusion coating method, a spin coatingmethod, a slit scan method, or the like can be used as a method ofarranging the liquid curable composition (A1) 102 onto the substrate 101or the layer to be processed, for example. In the present invention, aspin coating method is particularly preferable.

Before the liquid curable composition (A1) 102 is arranged onto thesubstrate 101 or the layer to be processed, a step is taken such thatthe content of the solvent component (d1) in the curable composition(A1) 102 film will be 10 wt % or less. To achieve this, it is preferableto perform a baking step as needed to volatilize the solvent component(d1). Note that it is preferable for the component (a), the component(b), and the component (c) to be low in volatility so that they will notvolatize in the baking step.

For the baking step, a known means such as an oven or a hot plate can beused. The baking condition can be performed under such a condition as 30to 200° C. and 1 to 600 seconds. It is preferable to appropriately setthe condition so as to volatilize the solvent component (dl) and keepthe component (a), the component (b), and the component (c) fromvolatilizing.

Note that the average film thickness of the curable composition (A1) 102is, for example, 0.1 nm or more and 1,000 nm or less, preferably 1 nm ormore and 50 nm or less, and particularly preferably 1 nm or more and 10nm or less, through it varies depending on the application.

Second Arranging Step [2]

In this step (second arranging step), as illustrated in FIG. 1C,droplets of a liquid curable composition (A2) 103 are arranged onto thelayer of the liquid curable composition (A1) described above by droppingthem discretely. An inkjet method is particularly preferable as anarranging method to drop droplets discretely. The volume of a droplet tobe dropped is 0.1 picoliter (pL) or more and 1,000 pL or less,preferably 0.1 pL or more and 100 pL, and particularly preferably 0.6 pLor more and 10 pL. When the total volume of droplets is the same, thesmaller the average droplet volume and the higher the dropletarrangement density, the smaller the interval of arranging droplets, sothat the droplets combine each other quickly, and the time taken by thesurface of the liquid film of the mixed liquid curable composition tobecome smooth in the later-described waiting step is short.

The film thickness of the liquid curable composition (A2) is defined asa value obtained by dividing the total volume of droplets of the liquidcurable composition (A2) by the area of the planarization area. Thisdefinition applies also to the case of mixing the liquid curablecomposition (A2) with the liquid curable composition (A1) arranged inthe first arranging step. According to this definition, the filmthickness of the mixed liquid curable composition is the sum of the filmthickness of the liquid curable composition (A1) and the film thicknessof the liquid curable composition (A2) based on the definition.

The film thickness of the liquid curable composition (A2) is, forexample, 10 nm or more and 1,000 nm or less, preferably 110 nm or moreand 500 nm or less, and particularly preferably 150 nm or more and 250nm or less. The larger the film thickness is, the smaller the fluidresistance to be received from the substrate surface, and thus thefaster the planarization in the later-described waiting step. The upperlimit value of the film thickness varies depending on the step(s) afterthe planarization method according to the present invention.

The droplets of the liquid curable composition (A2) 103 are arrangeddensely over regions where concavities on the substrate are densitypresent, and arranged sparsely over regions where concavities aresparsely present. By doing so, the mixed liquid curable composition isformed thickly over the concavities on the substrate and thinly over theconvexities on the substrate, so that the unevenness of the surface ofthe mixed liquid curable composition film are smaller than theunevenness of the substrate surface.

In the present invention, the droplets of the liquid curable composition(A2) 103 arranged in this step (second arranging step[2]) spread quicklyin the direction of arrows 104 due to the Marangoni effect using thedifference in surface free energy (surface tension) as driving force, asmentioned above, while being mixed with (A1) (FIG. 1D).

Waiting Step [3]

In the case where the first arranging step has been performed, thedroplets of the liquid curable composition (A2) spread while being mixedwith the liquid curable composition (A1), and combine with theneighboring droplets, and the surface of the liquid film of the mixedliquid curable composition becomes smoothed by the surface tension. Themixed liquid curable composition is caused to wait until its planereaches a desired degree of planarization (FIG. 1E).

In the case where the first arranging step has been omitted, the liquidcurable composition (A2) spread with its own surface tension andcombines with the neighboring droplets, and the surface of the liquidfilm of the liquid curable composition (A2) becomes smoothed by thesurface tension.

In the case where the first arranging step is omitted and thelater-described molding step is to be performed, the liquid curablecomposition (A2) is caused to wait until it covers 99% or more of thearea of the planarization area. If the covered region is less than 99%,gas will remain in gaps between the substrate, the liquid curablecomposition (A2), and a later-described mold in the later-describedmolding step, and will thus generate void defects.

The degree of planarization required varies depending on a lithographystep to be performed as a step following the planarization methodaccording to the present invention. For example, in the extremeultraviolet exposure technique (EUV), the depth of focus at which aprojected image is formed is about 4 nm, and therefore the heightdifference of the unevenness on the surface of the liquid film ispreferably about 4 nm or less. The planarization of the surface of theliquid film may require a time of about 0.1 second to 3600 seconds,though it varies depending on the liquid physical properties and thefilm thickness condition.

A heating step, a vibration application step, a substrate rotation step,or the like may be performed as a step of accelerating the planarizationas needed during the waiting step.

The atmosphere around the substrate during the wait may be air, or maybe an atmosphere of an inert gas such as nitrogen, carbon dioxide,helium, or argon.

Meanwhile, it is advantageous to perform a time-series measurement onthe flow behavior of the liquid curable composition arranged on a samplesubstrate under the same condition until the liquid curable compositionbecomes smoothed, and determine the necessary wait time. In this way,the predetermined wait time necessary for the planarization can beobtained in advance. Note that the liquid film of the mixed liquidcurable composition does not have to be smooth in the case where thelater-described molding step is to be performed.

Molding Step [3+]

In one embodiment of the present invention, a molding step aimed ataccelerating the planarization may be performed (FIG. 2E). This stepuses a mold 106 with a smooth surface that is to be in contact with amixed liquid curable composition film 105. While the waiting step may beperformed before the molding step is preformed, the liquid film of themixed liquid curable composition before the molding step does not haveto be smooth.

As the mold 106, a mold 106 made of an optically transmissive materialis advantageously used in consideration of the next step (light exposurestep). As the material of the mold 106, specifically, glass, quartz, anoptically transparent resin such as PMMA or a polycarbonate resin, atransparent metal vapor-deposition film, a soft film ofpolydimethylsiloxane or the like, a photocurable film, a metallic film,or the like is preferable. It is to be noted that in the case of usingan optically transparent resin as the material of the mold 106, it isnecessary to select a resin that does not dissolve in the componentscontained in the liquid photocurable compositions (A1) and (A2).

A surface treatment may be performed on the mold 106 before this step toimprove the releasability of the mixed liquid curable composition film105 and the surface of the mold 106 from each other. Methods for thesurface treatment include a method in which a release agent is coatedonto the surface of the mold 106 to form a release agent layer. Here,the release agent to be coated onto the surface of the mold 106 includesa silicone-based release agent, a fluorine-based release agent, ahydrocarbon-based release agent, a polyethylene-based release agent, apolypropylene-based release agent, a paraffin-based release agent, amontan-based release agent, a carnauba-based release agent, and thelike. For example, a commercially-available coating-type release agentsuch as OPTOOL DSX manufactured by DAIKIN INDUSTRIES, LTD can bepreferably used. One kind of the release agents may be used alone, ortwo or more kinds thereof may be used in combination. Among these, thefluorine-based and hydrocarbon-based release agents are particularlypreferable.

When the mold 106 and the liquid mixed photocurable composition 105 arebrought into contact with each other in this step (molding step), it ispreferable to press the mold 106 against the liquid mixed photocurablecomposition 105. The pressure to be applied to the liquid mixedphotocurable composition 105 by the mold 106 and the substrate is notparticularly limited. Advantageously, this pressure is 0 MPa or higherand 100 MPa or lower. Also, this pressure is preferably 0 MPa or higherand 50 MPa or lower, more preferably 0 MPa or higher and 30 MPa orlower, and further preferably 0 MPa or higher and 20 MPa or lower.

Further, the time for which the mold 106 is brought into contact withthe liquid mixed photocurable composition 105 in this step is notparticularly limited. Advantageously, this time is 0.1 second or longerand 600 seconds or shorter. Also, this time is preferably 0.1 second orlonger and 300 seconds or shorter, more preferably 0.1 second or longerand 180 seconds or shorter, and particularly preferably 0.1 second orlonger and 120 seconds or shorter.

While this step can be performed under any of conditions of an airatmosphere, a reduced pressure atmosphere, and an inert gas atmosphere,the reduced pressure atmosphere or the inert gas atmosphere ispreferable since it can prevent oxygen and moisture from affecting thecuring reaction. Specific examples of the inert gas usable in the caseof performing this step under the inert gas atmosphere include nitrogen,carbon dioxide, helium, argon, various chlorofluorocarbon gases, and thelike, and mixed gases thereof. In the case of performing this step underan atmosphere of a particular gas including the air atmosphere, apreferable pressure is 0.0001 atmosphere and higher and 10 atmospheresor lower.

Light Exposure Step [4]

Thereafter, as illustrated in FIG. 1F, light is applied to the mixedliquid curable composition 105, which a mixture of the liquid curablecomposition (A1) and the liquid curable composition (A2). In the casewhere the molding step has been performed, the light is applied throughthe mold (FIG. 2F). As a result, the mixed liquid curable compositionbecomes a cured film 108 having a smoother surface than the substratesurface.

Here, light 107 to be applied to the mixed liquid curable composition isselected according to the wavelengths which the liquid curablecompositions (A1) and (A2) are sensitive to. Specifically, it ispreferable to select and use ultraviolet rays with wavelengths of 150 nmor longer and 400 nm or shorter, X rays, electron rays, or the like asappropriate.

Among these, the ultraviolet rays are particularly preferable as theapplied light 107. This is because many of curing aids(photopolymerization initiators) that are commercially available arecompounds having sensitivity to ultraviolet rays. Here, examples of thelight source that emits the ultraviolet rays include a high-pressuremercury vapor lamp, an ultra-high-pressure mercury vapor lamp, alow-pressure mercury vapor lamp, a deep-UV lamp, a carbon arc lamp, achemical lamp, a metal halide lamp, a xenon lamp, a KrF excimer laser,an ArF excimer laser, an F₂ excimer laser, and so on, and theultra-high-pressure mercury vapor lamp is particularly preferable. Also,the number of light sources to be used may be one or be two or more.Further, the entire surface of the mixed liquid curable composition maybe irradiated or only a partial region(s) may be irradiated.

When at least one of the liquid curable compositions (A1) and (A2) isradical polymerizable, the atmosphere around the substrate during thelight application is preferably an atmosphere of an inert gas such asnitrogen, carbon dioxide, helium, argon, any of variouschlorofluorocarbon gases, or a mixed gas thereof in order to suppressoxygen inhibition.

Also, the light may be applied a plurality of times intermittently overthe entire region of the substrate or applied continuously over theentire region. Further, the light may be applied to a partial region Ain a first application step and applied to a region B different from theregion A in a second application step.

Releasing Step [5]

In an embodiment of the present invention, in the case where the moldingstep aimed at accelerating the planarization has been performed, areleasing step of detaching the mold is necessary (FIG. 2G). In thiscase, the cured film 108 having a smooth surface has been formed on thesubstrate 101.

The method of detaching the cured film 108 and the mold 106 from eachother is not particularly limited as long as it does not physicallydamage any part of the cured film 108 in the detachment, and variousconditions and the like are not particularly limited either. Forexample, the substrate 101 (substrate to be processed) may be fixed, andthe mold 106 may be moved away from the substrate 101 to be released.Alternatively, the mold 106 may be fixed, and the substrate 101 may bemoved away from the mold to be released. Still alternatively, both ofthem may be pulled in opposite directions to be released from eachother.

With a series of steps (production process) including theabove-described step [1] to step [4] or [5], a smooth cured film of themixed liquid curable composition can be formed on a substrate surfacehaving unevenness.

If the cured film is too thick, the surface of the cured film may beevenly etched back by a known etching technique such as dry etching orozone ashing.

In the planarization method according to this embodiment, the liquidcurable composition (A1) can be arranged on a most part of the substratesurface at once in step [1], and a repetition unit (shot) including thestep [2] to step [4] or [5] can be repetitively performed on the samesubstrate a plurality of times. Alternatively, the step [1] to step [4]or [5] may be repetitively performed on the same substrate a pluralityof times. By repeating a repetition unit (shot) including the step [1]to step [4] or [5] or the step [2] to step [4] or [5] a plurality oftimes, it is possible to obtain a smooth cured film of the mixed liquidcurable composition at desired positions on the substrate to beprocessed. Alternatively, each of the step [1] to step [4] or [5] may beperformed on the entire substrate surface at once.

By heating the smooth cured film of the mixed liquid curable compositionobtained through the step [1] to step [4] or [5] at a high temperatureof about 200 to 450° C. for about 10 to 600 seconds, it is possible toimprove the mechanical strength, dry etching resistance, heatresistance, and the like of the cured film.

If there is still unevenness remaining on the cured film of the mixedliquid curable composition obtained through the step [1] to step [4] or[5], the cured film may be smoothed by performing the step [1] to step[4] or [5] again. In the case of performing the step [1] to step [4] or[5] again, they may be the same as or different from those in theprevious embodiment. The step [1] to step [4] or [5] may be performedagain and again.

It is possible to perform a photolithography step by coating aphotoresist directly onto the smooth cured film of the mixed liquidcurable composition obtained through the step [1] to step [4] or [5].Alternatively, it is possible to perform a photolithography step bylaminating a spin-on-glass (SOG) film or a silicon oxide layer andcoating a photoresist onto it. Consequently, a circuit substrate to beutilized in a semiconductor device or the like can be fabricated. Also,by connecting this circuit substrate and a circuit control mechanism forthe circuit substrate and the like, it is possible to form an electronicinstrument, such as a display, a camera, or a medical apparatus.Examples of the semiconductor device mentioned here include an LSI, asystem LSI, a DRAM, a SDRAM, a RDRAM, a D-RDRAM, a NAND flash, and thelike.

EXAMPLES

The present invention will be described below in more detail by way ofexamples. However, the technical scope of the present invention is notlimited to the examples to be described below. Note that “parts” and “%”used below are based on weight unless otherwise noted.

Theoretical Calculation

Behavior in which droplets of the liquid curable composition (A2) aredropped onto a substrate on which a liquid film of the liquid curablecomposition (A1) is formed, and spread while being mixed, and furtherthe surface of the liquid film of the mixed liquid curable compositionis smoothed is theoretically calculated as below.

The model for the theoretical calculation is as below. All droplets ofthe liquid curable composition (A2) to be dropped are assumed to havethe same volume. An area obtained by dividing an entire area to whichthe planarization method according to the present invention is to beapplied by the total number of droplets is defined as a unit area. Aliquid film of the liquid curable composition (A1) is formed on acircular substrate having an area equal to the unit area. The substratesurface is assumed to be smooth. A coordinate system for the calculationis a radially finite cylindrical coordinate system having its origin atthe center of the surface of a unit circular substrate, and having awall boundary in contact at an angle of 90 degrees with thecircumference of the unit circular substrate. A single droplet of theliquid curable composition (A2) is dropped onto a center portion of theunit circular substrate, and spreads while being mixed with the liquidfilm of the liquid curable composition (A1) formed in advance. Thecalculation for the case where the liquid curable composition (A1) isomitted is approximated by, in order to maintain calculation stability,arranging a liquid film having the same values of the physicalproperties as the liquid curable composition (A2) sufficiently thinly (1nm or less) as compared to the liquid film thickness after theplanarization, and setting the surface tensions of the liquid curablecomposition (A1) and the liquid curable composition (A2) at an identicalvalue.

The Marangoni force originating from a surface tension gradientgenerated by a concentration distribution, and the Laplace thicknessgenerated by a thickness distribution in the in-plane direction areconsidered as illustrated in FIGS. 3 and 4 with a lubricationapproximation applied under the assumption that the concentration ratioof (A1)/(A2) in the direction of the liquid film thickness is constantand under the Reynolds assumption.

With the lubrication approximation, a time evolution equation of aliquid film height h is expressed as below using a pressure p, a surfacetension σ, and a viscosity μ.

$\begin{matrix}{\frac{\partial h}{\partial t} = {\nabla \cdot ( {{\frac{h^{3}}{3\mu}{\nabla p}} - {\frac{h^{2}}{2\mu}{\nabla\sigma}}} )}} & {{equation}(1)}\end{matrix}$

In an axisymmetric model as illustrated in FIG. 4 , the above equation(1) can be transformed as below.

$\begin{matrix}{{r\frac{\partial h}{\partial t}} = {\frac{\partial}{\partial r}( {{\frac{rh^{3}}{3\mu}\frac{\partial p}{\partial r}}\  - \ {\frac{rh^{2}}{2\mu}\frac{\partial\sigma}{\partial r}}} )}} & {{equation}(2)}\end{matrix}$

Here, the pressure p is a Laplace pressure

$\begin{matrix}{p = {- {\sigma\lbrack {\frac{\frac{\partial^{2}h}{\partial r^{2}}}{( {1 + \frac{\partial h}{\partial r}} )^{\frac{3}{2}}} + \frac{\frac{\partial h}{\partial r}}{r\sqrt{1 + ( \frac{\partial h}{\partial r} )^{2}}}} \rbrack}}} & {{equation}(3)}\end{matrix}$

considered up to the secondary order for discretization. Here, the firstterm represents a Laplace pressure by a curvature in a radial direction,and the second term represents a Laplace pressure by a curvature in anargument direction.

Further, with a diffusion coefficient D of the droplets of the liquidcurable composition (A2) and the liquid film of the liquid curablecomposition (A1), an advection-diffusion equation at a concentration ccan be expressed as below using a speed vector {right arrow over (u)}averaged in the height direction.

$\begin{matrix}{{\frac{\partial( {ch} )}{\partial t} + {\nabla \cdot ( {\overset{arrow}{u}ch} )}} = {\nabla \cdot \{ {D{\nabla( {ch} )}} \}}} & {{equation}(4)}\end{matrix}$

In the axisymmetric model, this equation 4 can also be transformed asbelow using a speed u in the radial direction averaged in the heightdirection.

$\begin{matrix}{{{r\frac{\partial( {ch} )}{\partial t}} + \frac{\partial( {urch} )}{\partial r}} = {\frac{\partial}{\partial r}( {rhD\frac{\partial c}{\partial x}} )}} & {{equation}(5)}\end{matrix}$

By simultaneously solving the equation 2 and the equation 5, it ispossible to obtain time evolution c(r, t) of the concentrationdistribution and time evolution h(r, t) of the liquid film heightdistribution in the axisymmetric model.

Liquid film height distribution profiles were calculated for variousconditions of viscosity, surface tension, film thickness, and dropletvolume as listed in tables 1 to 5. The diffusion coefficient D wasassumed to be 1×10⁻⁹ (m²/s) for both the liquid curable composition (A1)and the liquid curable composition (A2). Note that it is to beunderstood that the film thickness of (A2) is equal to the volume of adroplet x the number of droplets/the area of planarization area.

From the calculated liquid film height distribution profiles, the heightdifferences on the liquid film surfaces 300 seconds after the droppingof the droplets were measured and listed in tables 1 to 5.

TABLE 1 Compar- Compar- ative ative Exam- Exam- Exam- Exam- ple 1 ple 2ple 1 ple 2 Viscosity [mPa · s] (A1) 200 200 200 200 (A2) 30 30 30 30Surface Tension (A1) 30 31 33 35 [mN/m] (A2) 30 30 30 30 Film Thickness[nm] (A1) 40 40 40 40 (A2) 20 20 20 20 Total 60 60 60 60 Droplet Volume[pL] 1 1 1 1 Largest Height Difference 300 140 35 50 [nm] on Liquid FilmSurface 300 Seconds after Dropping

TABLE 2 Exam- Exam- Exam- Exam- ple 3 ple 4 ple 5 ple 6 Viscosity [mPa ·s] (A1) 200 200 200 200 (A2) 30 30 30 30 Surface Tension (A1) 35 35 3533 [mN/m] (A2) 30 30 30 30 Film Thickness [nm] (A1) 30 40 50 30 (A2) 3020 10 30 Total 60 60 60 60 Droplet Volume [pL] 1 1 1 1 Largest HeightDifference [nm] on 40 50 55 50 Liquid Film Surface 300 Seconds afterDropping

TABLE 3 Compar- ative Exam- Exam- Exam- Exam- ple 7 ple 3 ple 8 ple 9Viscosity [mPa · s] (A1) 200 200 200 200 (A2) 30 30 30 30 SurfaceTension (A1) 33 33 33 33 [mN/m] (A2) 30 30 30 30 Film Thickness [nm](A1) 20 10 10 10 (A2) 40 50 150 250 Total 60 60 160 260 Droplet Volume[pL] 1 1 1 1 Largest Height Difference [nm] 70 160 <4 <4 on Liquid FilmSurface 300 Seconds after Dropping

TABLE 4 Exam- Exam- Exam- Exam- ple 10 ple 11 ple 12 ple 13 Viscosity[mPa · s] (A1) 200 200 200 — (A2) 30 30 30 30 Surface Tension (A1) 33 3333 — [mN/m] (A2) 23 28 33 33 Film Thickness [nm] (A1) 10 10 10 0 (A2)150 150 150 150 Total 160 160 160 150 Droplet Volume [pL] 1 1 1 1Largest Height Difference [nm] <4 <4 <4 <4 on Liquid Film Surface 300Seconds after Dropping

TABLE 5 Example 14 Example 15 Viscosity [mPa · s] (A1) — 200 (A2) 30 30Surface Tension [mN/m] (A1) — 33 (A2) 33 28 Film Thickness [nm] (A1) 010 (A2) 250 110 Total 250 120 Droplet Volume [pL] 1 1 Largest HeightDifference [nm] <4 20 on Liquid Film Surface 300 Seconds after Dropping

Liquid films of mixed liquid curable compositions having thicknesses of160 nm and 260 nm and having a planarization of <4 nm are obtained inexamples 8 and 9, respectively. In other words, by evenly arranging a 10nm-thick liquid film of the liquid curable composition (A1) onto asubstrate having unevenness whose largest height difference is 100 nmand appropriately arranging 1-pL droplets of the liquid curablecomposition (A2) at high density over the concavities and at low densityover the convexities, it is possible to obtain a smooth liquid filmsurface whose largest height difference is less than 4 nm.

In examples 13 and 14, the first arranging step is omitted, that is, thefirst liquid curable composition (A1) is omitted. In each of these casestoo, a smooth liquid film surface whose largest height difference isless than 4 nm can be obtained. Thus, it is possible to obtain a smoothliquid film surface whose largest height difference is less than 4 nmover a substrate having unevenness whose largest height difference is100 nm.

In examples 1 to 7 too, the largest height difference on the liquid filmsurface is 100 nm or less, which is less than those in comparativeexamples 1 to 3. Even under the conditions of examples 1 to 7, it ispossible to obtain a liquid film surface whose largest height differenceis 100 nm or less over a substrate having unevenness whose largestheight difference is 100 nm.

Experiment

Droplets of the liquid curable composition (A2) having a viscosity of7.0 mPa·s and a surface tension of 34 mN/m were dropped by 1.0 pL eachonto a smooth silicon substrate discretely at predetermined intervals ina lattice-like arrangement (in X-Y directions). After waiting apredetermined time, it was cured by irradiation with ultra-violet lightfrom an ultra-high pressure mercury lamp to form a cured film. Heightdifference of the cured film surface was measured by using a SURFCORDER(mfd. by Kosaka Laboratory). Measurement results are shown in Table 6.

TABLE 6 Comp. Comp. Comp. Comp. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 16 DropletVolume (pL) 1.0 1.0 1.0 1.0 1.0 Y-direc. Interval (μm) 70 70 70 70 70X-direc. Interval (μm) 70 70 70 70 70 Film Thickness (nm) 204 204 204204 204 Waiting Time (s) 0 15 30 60 120 Largest Height Diff.of >20 >20 >20 >20 6 Cured Film Surf. (nm)

As seen above, Example 16 has demonstrated that a smooth cured film ofthe liquid curable composition (A2) can be obtained even when themolding step of contacting a smooth mold is omitted.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A planarization method comprising: arranging aliquid curable composition onto a substrate having unevenness; bringinga contacting member, which has a smooth surface over a contact region,into contact with the liquid curable composition on a surface of thesubstrate; curing the liquid curable composition to form a curedcomposition; and releasing the contacting member from the curedcomposition, wherein the liquid curable composition contains at least apolymerizable compound, and wherein the arranging the liquid curablecomposition onto the substrate includes: dropping droplets of the liquidcurable composition discretely; and waiting without contacting thecontacting member until the droplets flow to spread over the substratesuch that the liquid curable composition covers 99% or more of an areaof a planarization area, wherein the waiting is such that the dropletsof the liquid curable composition spread and combine with neighboringdroplets.
 2. The planarization method according to claim 1, wherein: anaverage volume of the droplets of the liquid curable composition is 0.1picoliter (pL) to 100 pL; and a value obtained by dividing a totalvolume of the droplets by an area of a planarization area is 150 nm orless.
 3. The planarization method according to claim 1, wherein thesubstrate having unevenness has concavities measuring 1 to 1,000 nm indepth and 1,000 um or less in width and being larger in width than indepth.
 4. The planarization method according to claim 1, wherein thedroplets of the liquid curable composition are dropped densely over aportion where concavities on the substrate are dense, and droppedsparsely over a portion where concavities on the substrate are sparse.5. The planarization method according to claim 1, wherein a volume of adroplet of the liquid curable composition is 0.1 picoliter (pL) to 100pL.
 6. The planarization method according to claim 1, wherein a liquidfilm thickness of the liquid curable composition before curing is 150 nmor more on a portion of the substrate where the liquid curablecomposition is thinnest.
 7. The planarization method according to claim1, wherein a surface tension of the liquid curable composition is 20mN/m to 40 mN/m.
 8. The planarization method according to claim 1,wherein the waiting is to obtain a smooth liquid film surface of theliquid curable composition with a largest height difference of less than4 nm.
 9. A planarization method comprising performing the planarizationmethod according to claim 1 on a same portion of the substrate aplurality of times.